The present invention relates to an IP device which can register access data in a management server by being connected to a router and assigned with a port number for port forwarding, a management server which registers this access data and provides address data of this IP device to a terminal that accesses via a wide area network, and a network system comprising these.
ADSL and CATV for constant connection to a wide area network such as the Internet have spread on a full scale, and broadband routers have widely spread. However, with the current IP protocol IPv4, the absolute number of global IP addresses is insufficient, so that the shortage of global IP addresses is covered by using the NAT (Network Address Translation) function and the port forwarding function (static IP masquerade). This NAT function converts a local IP address of a LAN-side device into a global IP address of the WAN side of a router when the LAN-side device accesses the Internet.
Furthermore, when access is made to a specific device on the LAN side from the Internet, the access can be made by using a port forwarding function (static IP masquerade) of a router. Namely, for this, a conversion table of port numbers and local IP addresses must be set in the router in advance. When access is made from the Internet, a global IP address and a port number of the router are specified. The router that has accepted this access converts the global IP address into a local IP address according to the conversion table set in advance. By this conversion, access can be made to one device having the local IP address within a LAN from the Internet.
Thus, a conventional router connects a plurality of user devices and the Internet by alleviating the exhaustion of global IP addresses by the port forwarding function and the NAT function, however, a user must know the port number of the LAN side device and manually set and change it.
Therefore, by the UPnP forum, standards for dynamic port forwarding (port mapping) are created (refer to UPnP standards). In the settings of the standards, a subordinate terminal inquires to a router whether or not a port is usable, and when it is usable, the router registers it, and when it is unusable, the terminal inquires whether or not the port is usable again, and this is repeated until usability is determined. According to the UPnP standards, a manual port forwarding setting is not necessary, and the port number of the Internet side can be automatically set without depending on the vendor of the router.
The UPnP standards can be browsed at URL: http://www.upnp.org/standardizeddcps/default.asp (searched on Nov. 29, 2002).
However, since the port number is automatically selected, a user on the Internet side cannot know which port number is assigned to which of the terminals. In order for a user on the Internet side to access a device on the LAN side, he/she must know the port number thereof. From the inside of the LAN, port numbers to be used by each of the terminals can be confirmed by using a user interface (web page) of a router or a terminal, however, from the Internet side (outside), a user interface of a router cannot be used by reason of security.
Therefore, the present applicant proposed a method in which, when a plurality of IP devices exist under the router and make communications by being assigned with ports, respectively, according to the UPnP standards, a representative device is selected among the devices and made to manage address data and provide address data of other devices for access from a wide area network (Japanese Patent Application No. 2003-12241, equivalent to U.S. patent application Ser. No. 10/760,552). For example, a representative device is selected among a plurality of IP devices (for example, network cameras) under a router, and is provided with a fixed port number “80.” Thereby, by accessing the representative device from a wide area network side, access to other devices becomes possible.
However, when images of the plurality of network cameras are browsed from a client terminal, the terminal must access the network cameras one by one, and the access time becomes long and this is troublesome and inconvenient. Therefore, it is convenient if a plurality of images can be displayed at a time in a list and image data can be acquired from the network by accessing by using the list. For example, conventionally, a system for displaying a list of thumbnails of a plurality of images has been proposed (Japanese Unexamined Patent No. 2002-82957).
Furthermore, an image communications method has also been proposed in which a desired image is selected while displaying a plurality of images (Japanese Unexamined Patent No. 2002-351771). In this method, when a client sends a request while any of the images held by an image server are displayed or the images are displayed in order, the image server sends the image being displayed to the client.
As described above, the conventional port forwarding function (static IP masquerade) of a router can make access to a LAN side device by using a port number, however, a user on the Internet side must know the port number of the LAN side device, and when the port number is changed due to a system change on the LAN side, the change must be manually followed up.
Furthermore, when port forwarding setting is dynamically made according to the standards of the UPnP forum, a terminal inquires to a router whether a port is usable, and when it is usable, it is registered, and when it is unusable, the terminal repeatedly inquires, however, the router automatically selects a port number, so that a user on the Internet side cannot know which of the port numbers is assigned to the terminal.
The present applicant also proposed an access method by using a representative device, however, in the access method, the port number of the representative device must be fixed, and when a fixed port number is unusable, access to the representative device is impossible, and as a matter of course, access to all devices becomes impossible. For example, a port number “80” is used for communications by HTTP, however, in a case where this port number is reserved by a router for another use, this port number cannot be assigned to the representative device, so that access becomes impossible.